Cutting insert and tool having a cutting insert

ABSTRACT

A cutting insert suitable for the milling of gray cast iron has a cutting corner defined between two angularly adjoining cutting edges at junctions between a rake face formed on one of the sides and respective clearance faces extending between the sides, a spherically segmental indentation being formed in the rake face at the corner and intersecting the cutting edges with respective arcs where the cutting edges adjoin at the corner, the cutting edges being linear over stretches thereof extending away from the arcs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/DE99/103785 filed Nov. 25,1999 and based upon German application 298 22 553.0 filed Dec. 18, 1998under the International Convention.

FIELD OF THE INVENTION

The invention relates to a cutting insert for the machining ofworkpieces, especially the roughing-finishing machining of gray castiron by surface milling and wherein the rake surface is bounded bycutting edges of which two mutually-adjacent cutting edges form acutting corner, the cutting insert having at least one trough-shapedindentation interrupting the cutting edges.

The invention relates further to a tool comprised of a tool holder withat least one recess for receiving such a cutting insert.

BACKGROUND OF THE INVENTION

Milling machining is generally carried out in two working steps, apremilling (roughing) and a fine milling. A combined roughing-finishingtool can be provided which has a part of the cutting inserts clamped inthe recesses (seats) provided in the tool holder utilized as purelyroughing tools and the remainder utilized as finishing tools. Examplesfor finishing cutting inserts are described in DE 197 03 569. Thecutting inserts there described, which preferably have rake faces asregular hexagons, comprise a plurality of main cutting edges andauxiliary cutting edges connected thereto. As has been described in thispublication, a cutting insert of that type can be used in combinationwith a cutting insert for roughing.

The cutting inserts described in DE 197 03 569 A1 have in conjunctionwith the auxiliary cutting edges a concave chip-forming groove whoseradius is between 0.5 mm and 0.8 mm. With this chip-forming groove thecutting angle of the auxiliary cutter should be set between 10° and 20°.A chip-forming groove also extends along the main cutting edges and incross section has a radius of curvature of 0.5mm measured in crosssection. This publication does not describe purely roughing turninginserts.

A cutting insert is known from DE 28 40 610 C2 which has indentations inthe rake face along the cutting edges and of a width whose greatestdimension is parallel to the cutting edges and which is greater than thedistance between two neighboring indentations. Each of theseindentations interrupts the cutting edge which here has a shape whichchanges in the region of the interruption, i.e. no longer forms astraight line, but rather in the region of the interruptions has aconfiguration rearwardly of the straight line cutting edge parts in thechip travel direction. Because of these features, buckling is producedin the chip travelling away from the cut which serves to break up thechip into short pieces. The region of the cutting corner should howeverbe free from indentations and instead should have a planar rake surfaceportion or a negative consolidation surface to avoid an increase in thetendency toward buckling of the chip in the corner region. The mentionedindentations can, according to DE 28 40 610 C2, also be arranged in achip-forming trough running along the cutting edge. In thesepublications a trigonally-shaped cutting insert is described which isunsuitable for rough milling operations.

U.S. Pat. No. 4,710,069 describes a cutting insert which has along itscutting edges a chamfer and in the region of the chamfer remote from thecutting edge, a groove-like recess. The boundary line between thementioned chamfer and the groove-like recess is interrupted by amultiplicity of equally spaced recesses whose depths should be less than0.1 mm. The recesses are substantially partially spherical recesses witha radius of curvature of 0.5 mm. Such cutting inserts are however onlysuitable for turning-type machining operations.

The shapes of roughing-finishing inserts which have been provided up tonow have respective chip-forming troughs in conjunction with the cuttingedges and extending over their entire lengths. In the region of acutting edge corner, this chip-forming trough is interrupted byrelatively higher lying stiffening surfaces. The roughing-finishingmachining is however carried out with cutting depths of approximately0.5 mm to 1 mm. Thus the rounded cutting corner effects cutting so thata modification of the chip-forming groove to increase the chip-formingangle does not yield any effective improvement. Moreover, a lengtheningof a chip-forming groove in the cutting corner region while reducing thewidth of the stiffening surfaces readily reaches limits since remainingsharp edged projections, especially in the cutting corner region, tendto crumbling which significantly reduces the life of the cutting insert.

OBJECT OF THE INVENTION

It is thus an object of the present invention to provide a cuttinginsert for roughing-finishing and with which the axial forces arising inmilling use are significantly reduced.

SUMMARY OF THE INVENTION

This object is achieved, according to the invention, by a cutting insertin which the indentations are arranged in the cutting-corner regions andinterrupt both of the cutting edges which adjoin there.

In contrast to the teaching disclosed in DE 28 40 610 C2, to the effectthat the cutting corner region should be left free from trough-likedepressions or indentations, the cutting inserts formed according to theinvention show significantly reduced cutting forces and a resultingimproved life by comparison with the previous cutting inserts. Throughthe use of a spherical segmental recess in the cutting corner regions,significantly larger chip angles are permitted and for a cutting insertclamped in a tool holder greater effective radial and axial chip anglescan be realized. The cutting edges which are linear except in thecutting corner regions are, as a result of the indentations, concavelycurved at their rear parts in the direction of the cutting corners andthe cutting corners lie approximately at the height or level of thelinearly running cutting edge or slightly therebelow. This is repeatedin a corresponding manner whereever the cutting edges adjoin the cuttingcorners. The cutting insert is used in milling in that preferably thecutting edge portions falling away in a concave manner at both sides ofthe cutting corners are effective for cutting purposes. The maximumwidth of the indentations in the cutting corner region depends upon thedesired cutting depth. In the region of the cutting corner which iseffective for the cutting operation, a trough can be formed which allowsthe positive cutting angle to be optionally selected.

Preferably the indentations are symmetrical to the angle bisectors ofthe cutting corners.

According to a further feature of the invention, the indentations areformed in part as spherically segmental, whereby the radius of curvatureof the concave indentations lies between 4 mm and 10 mm. The maximumdepth of the indentations should preferably not be greater than 0.4 mmto 0.6 mm.

Since the cutting corners should only be used to an effective cuttingdepth of 0.5 mm to 1 mm, the maximum diameter of the indentation shouldbe 4 mm.

To maintain a sufficient cutting corner stability, the cutting angle γshould lie between +5° and +20° in the cutting corner region, preferablybetween +8° and +15°.

So that the cutting insert can be used not only on one side but also onthe top surface as well as the bottom surface, a central rake faceplateau can be provided for two-sided support, the cutting edge planesprojecting over the rake surface plateau. The intermediate cuttingsurface plateau has, according to a further feature of the invention,nose-shaped projections which extend into the rearward region of theindentations.

Preferably the cutting inserts of the invention are of regularsix-corner form in which the respective mutually adjacent cutting edgesare oriented at an obtuse angle of 120°. The cutting edges are roundedso that, according to a feature of the invention, the cutting cornerrounding has a radius between 0.4 mm and 3 mm. As has already beenindicated, the cutting insert is configured to be useful on both sidesso that twelve usable cutting corners are provided for machining.

The cutting insert according to the invention is preferably received ina recess or seat provided therefor in a tool holder configured as amilling tool body and are fastened in the recess. For fastening,clamping wedges can be used for fixing the cutting insert with respectto the tool axis. It is, however, also possible to arrange the cuttinginserts in cassettes which can then be affixed in the tool carrier inthe desired orientations. According to the invention, an orientation ofthe cutting insert for roughing is selected in which it has an effectiveaxial cutting angle γ_(p) of +5° to +10° and/or an effective radialcutting angle of 0° to +8° in the cutting insert recess.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention is shown in the drawing.

In the drawing:

FIG. 1 is a perspective view of a turning cutting plate according to theinvention as seen from the front;

FIG. 2 is a partial perspective section through this turning cuttingplate;

FIG. 3 is a perspective view of a turning cutting plate with respect toits mounted orientation;

FIGS. 4 and 5 are partial perspective views of the turning plateaccording to the invention for showing the cutting angle in the cornerregion;

FIG. 6 is a view similar to FIG. 5 for a milling insert;

FIGS. 7 and 8 are fragmentary perspective views of a cutting cornerregion for illustrating the spherical segmental configuration andorientation;

FIG. 9 is a fragmentary perspective view of the cutting corner to showthe cutting corner cutting angle γ at the rake surface; and

FIG. 10 is a fragmentary perspective view for illustrating the radialcutting angle.

The cutting insert 11 shown in the drawing is comprised of a regularsix-cornered rake surface which is bounded by six cutting edges 12 ofwhich two mutually adjacent cutting edges 12 form a cutting corner 13.The cutting corners 13 are rounded such that the cutting edges haverespective planar clearance faces 14 and the corners adjoin roundedclearance face segments 15. On the rake face the cutting insert has acentral rake face plateuu 16 which is star-shaped and has respectivenose-shaped projections 17 projecting in the direction of the cuttingcorners. Between two cutting corners, further projections 18 arearranged which are oriented approximately at the center of therespective cutting edges 12. The cutting insert 11 comprises, accordingto the invention, spherically segmental indentations 19 in each cuttingcorner on the rake face. The indentation 19 intersects the cutting edges12 with respective arcs 19 a, 19 b where the cutting edges adjoin at therespective corner (FIG. 2). A chip-forming groove 20 runs parallel toeach of the cutting edges 12 except in the regions of the sphericallysegmental indentations 19. The cutting edges have linear stretches 12 aextending away from the indentation 19. As can be deduced expeciallyfrom FIG. 1, the nose-shaped projections 17 and 18 are each comprised ofa lower concave part and an upper convex part. The projections can,however, comprise planar descending flanks or convex or concave flanks.The cutting insert has a thickness of, for example, 5.56 mm and aninscribed circle diameter of 16.2 mm. The cutting insert which isconfigured to be double-sided is preferably used for milling in a toolholder 100 (FIG. 2) which rotates about the rotation axis 21 (FIG. 3).The cutting insert 11 travels along the milling radius R_(f) so that thecutting insert is moved in the direction of the arrow 22 along withother rough cutting inserts. The machining operation which is carriedout is shown in greater detail in FIG. 6. The workpiece 23 is machinedwith an end surface miller with a cutting depth a_(p), whereby aplurality of roughing cutting inserts come into play.

In this milling operation a positive axial cutting angle γ_(p) isprovided via the aforedescribed segmental configuration (see FIG. 4).FIG. 5 shows a cutting angle γ₀, referring to a cutting depth a_(p) offor example 10.5 mm at a distance b of about 0.5 mm from the cuttingedge over a length which corresponds approximately to the selected 0.5mm tooth feed.

From FIG. 7 it will be clear that the indentation 19 forms a sphericalsegment. The sphere or partial sphere 24 can be seen from FIG. 7.

The corresponding spherical radius R_(k) lies between 4 mm and 10 mm andthe maximum segment depth t has a value between 0.4 mm to 0.6 mm.

FIG. 9 shows the cutting angle or rake angle γ at which the rake surfaceregion bounding the straight line part of the cutting edge 12 isinclined. The radial rake angle γ_(f) which is given by the mounting ofthe cutting insert in the tool holder is shown in FIG. 10.

A mill provided with cutting inserts 11 is used for the cutting of aworkpiece 23. By contrast to the conventional six-cornered turningcutting plates of the state of the art, there is a reduction in thepassive force of about 40%.

What is claimed is:
 1. A cutting insert suitable for the milling of graycast iron, comprising a generally flat cutting-insert body of polygonalshape and opposite sides, said body being formed along at least one ofsaid sides with a cutting corner defined between two angularly adjoiningcutting edges at junctions between a rake face formed on said one ofsaid sides and respective clearance faces extending between said sides,a spherically segmental indentation being formed in said rake face atsaid corner and intersecting said cutting edges with respective arcswhere said cutting edges adjoin at said corner, said cutting edges beinglinear over stretches thereof extending away from said arcs.
 2. Thecutting insert according to claim 1 wherein the indentation issymmetrical with respect to a cutting corner angle bisector.
 3. Thecutting insert according to claim 2 wherein the indentation has a radiusof curvature (RF) between 4 mm and 10 mm and a depth of 0.4 to 0.6 mm.4. The cutting insert according to claim 3 wherein said indentation hasa diameter (d) of a maximum of 4 mm.
 5. The cutting insert according toclaim 4 wherein said rake surface forms a rake angle between +5° and+20° at the cutting corner.
 6. The cutting insert defined in claim 5wherein said rake angle is +8° and +15°.
 7. The cutting insert accordingto claim 5 wherein said one of said 'sides has a central rake surfaceplateau and plurality of said cutting corners at vertices of a regularpolygon, said plateau being formed by a ridge formed with nose-shapedprojections rearwardly of the indentations of said corners.
 8. Thecutting insert according to claim 7, wherein said body has a regularsix-corner shape.
 9. The cutting insert according to claim 8 wherein thecutting corners are rounded with a radius between 0.4 mm and 3 mm.
 10. Atool comprised of a tool holder with at least one recess for receiving acutting insert according to claim 9 and wherein the cutting insert isarranged with an effective axial cutting angle of +5° to +10°.
 11. Acutting tool comprising a milling tool holder having at least onecutting-insert recess, and a cutting insert in said recess comprising agenerally flat cutting-insert body of polygonal shape and oppositesides, said body being formed along at least one of said sides with acutting corner defined between two angularly adjoining cutting edges atjunctions between a rake face formed on said one of said sides andrespective clearance faces extending between said sides, a sphericallysegmental indentation being formed in said rake face at said corner andintersecting said cutting edges with respective arcs where said cuttingedges adjoin at said corner, said cutting edges being linear overstretches thereof extending away from said arcs.